Many vehicles have several different passenger restraint mechanisms that are operable in the event of emergency conditions. When an emergency condition is detected, retractor locks are operable to block further payout of belt webbing from the retractor spool. Pretensionsers may be operable to eliminate slack in the seat belt webbing. Airbags may be deployed both inside and outside of the vehicle to protect both passengers and pedestrians. It is important that these various restraint systems have their operation properly synchronized to provide the most effective restraint to passengers in the vehicle compartment. In some instances, it is also desirable to have the systems disabled. In particular, due to the force with which an airbag may deploy, it is usually not desirable for the airbag to be operable if a very small adult or child is in the vehicle seat associated with the airbag.
In this regard, various sensor systems have been proposed to attempt to accurately weigh the seat occupant to discern whether the occupant is in the lower 5 percentile range of weights for females such as a small child so that operation of the airbag can be disabled. One significant difficulty arises due to the downward tension forces generated by the secured seat belt about the occupant. The seat belts in active systems are usually automatically retracted on the spool of retractors with a rewind spring mechanism so that cinching of the belt about the occupant generates tension forces, particularly in the lap belt portion that tend to push the occupant downwardly into the vehicle seat. It will be appreciated that this problem is exacerbated when an auxiliary child or booster seat is placed on the vehicle seat. In this instance, the increased height of the auxiliary seat is such that cinching of the seat belt over the child and auxiliary seat adds even more downwardly directed tension force than would be present if the child were seated directly on the vehicle seat without the auxiliary seat thereon.
Several solutions have been proposed to address the tension forces generated by the secured seat belt. In some instances, these solutions provide for specific locations for the seat weight sensors (SWS) and/or utilize belt tension sensors (BTS) in the seat belt in an attempt to compensate for the seat belt tension. Other solutions also employ vision-type detector systems that attempt to determine whether a child seat is present by the detected size and distance from the sensor object is on the seat. Several propose relatively complex algorithms for interpreting the data received from the sensors. Perhaps the simplest solution has been to place both of the lower anchors in a three-point active, seat belt system, for instance, on the seat frame just above the seat weight sensors so that the downward forces generated by the secured seat belt on the seat occupant are offset by the upward forces generated at either side of the seat on the anchors.
Active, door-mounted seat belt systems provide the advantage of keeping all the seat belt systems components but the buckle and its anchor out of the passenger compartment when the seat belt is not in use. In these systems, the retractor and the shoulder anchor are both mounted to the door. The lower, outboard anchor for the three-point door-mounted belt system is also mounted to the door. In many newer model vehicles, these active, door-mounted seat belt systems are highly desirable to provide more of an open cabin feel in the vehicle passenger compartment. Putting the lower, outboard anchor on the seat frame to compensate for belt tension forces on the seat occupant is not a good option as it can detract from the desired open cabin feel. More importantly, such a placement of a permanent anchor point for the belt in the passenger compartment such as on the vehicle seat frame creates a length of webbing that extends from the vehicle interior to the door even when the door is open making passenger ingress and egress from the vehicle more difficult and providing the vehicle with undesirable aesthetics. Thus, for these active, door-mounted seat belt systems, the prior art solutions focus on the use of weight and tension sensors, vision detection systems and/or complicated algorithms to determine the presence of a very small adult or child on a vehicle seat rather than creating the problems discussed above with moving the lower, door anchor to the vehicle seat frame.
Accordingly, there is a need for a door-mounted seat belt system that has a simple mechanism for compensating for seat belt tension. Further, the door-mounted system should not present an obstacle to passenger ingress and egress from the vehicle when the door is open.